Change in internal diameter due to temperature increase.?

The first three answers are correct, but confusing. Let me see if I can't simplify this for you.

The pipe expands in all directions. Assume that the pipe is made of a uniform material, like copper, so we can say that it expands uniformly in all directions.

You must understand that the metal expands uniformly per unit of measurement. Think of a strip of metal, first. (our piece of tubing cut down the side and unrolled flat.) This means not only that the length, width and thickness expand-- it also means that it will expand so much PER UNIT.

Suppose the copper will expand 1 mm per cm. (We'll use metric, just to keep it simple, because everything will be in tens.)

If the thickness of the copper strip is 1 cm,

it will expand to 1.1 cm, or 1 cm plus (1 x 1mm.)

If the width of the strip is 20 cm,

it will expand to 22 cm, or 20 cm plus (20 x 1 mm.)

If the length of the strip is 200 cm,

it will expand to 220 cm, or 200 cm plus (200 x 1 mm.)

Now, suppose we roll the strip back into a tube again.

The inner circumference of the tube started out as 20 cm, and the diameter was 20/ pi (which is something less than six cm.)

The new inner circumference is 22 cm, and the new diameter is 22/pi, which is greater than seven cm.

So, the metal expands proportionately in all dimensions, and the with of the strip (the circumference of the tube, and thus the diameter) expands MUCH MORE than the thickness of the strip, (which is the same as the tube wall).

Is physics cool, or what?

10 NOV 06, 0419 hrs, GMT.

Exactly, the inside has to expand - in order to maintain a circular shape as the material expands (most pipes are made of thin material that is rolled - so the change in thickness is negligible compared to the change in length). Imagine if you cut the pipe and rolled it flat, then heated it, and rerolled it, it would have a thicker diameter, because the material stretched (and yes the thickness did increase as well but not anywhere near as much as the length and width increased). You will also have a slightly longer pipe as compared to preheated.

What would happens to that region of metal if it were simply the outer layer of a cylinder? Or think of it this way. What happens to the circumference of the inside of the pipe as the pipe heats up? If the circumference of the inside of the pipe expands, then the inside diameter is increasing.

Hi. Heat expands materials. To shrink the ID would require a contraction.

No, the ID increases as well (the entire piece expands in all directions). That's how fitters achieve interference fits when assembling metal parts.